The present invention relates to an inclination angle sensor, to a method of sensing angles of inclination, and to a device (particularly an underground drilling or rock-piercing tool) employing an angle sensor.
WO88/06716 and JP-A-60/100712 disclose inclination angle sensors employing annular containers partly filled with a ferromagnetic or conductive fluid, e.g. mercury. The container is mounted in a vertical plane. Coils are wound about lower regions of the container, one on each side of the vertical diameter. The inductance of each coil is affected by the presence of the fluid within it. Thus when the container is tilted about its horizontal axis, the relative inductances of the coils vary. This is used to monitor the tilting.
Such devices are rather restricted in their application. Clearly, if tilting also occurred about an axis parallel to a horizontally extending diameter, e.g. so that the annulus became horizontal, the sensor would not work properly. Furthermore it is not very sensitive to small changes in inclination.